Examples of an existing method of operating a blast furnace include a technology described in Japanese Unexamined Patent Application Publication No. 5-186811. The technology involves counting the frequency of falling of an unmelted ore at a tuyere unit from thereabove and adjusting the ratio of ore and coke in an area around the furnace top from which the ore and coke are charged so that the frequency is kept from exceeding a predetermined reference value. The number of times the unmelted ore falls is counted through a monitor using a camera disposed at the blast furnace tuyere unit as the frequency or number of times that the brightness decreases in an image is counted as the frequency.
The technology described in Japanese Unexamined Patent Application Publication No. 5-186811, however, is to detect falling of unmelted ore at the tuyere unit and not to detect an abnormality causing clogging of the tuyere due to a flow of slag, molten iron, or other objects. Moreover, since the above-described technology exclusively determines the decrease in brightness in an image, the technology cannot detect a sudden change in brightness as a result of clogging of the tuyere distinguishably from a gradual change in brightness due to a temperature change in the raceway unit.
Thus, it could be helpful to provide a method of detecting an abnormality at a blast furnace with which an abnormality causing clogging of a tuyere can be detected at an early stage and a method of operating a blast furnace using the method of detecting the abnormality.